The present invention relates to monitoring systems. In particular, the invention concerns a method, system and terminal equipment for line monitoring, i.e. for technical monitoring of a line between two points.
For remote-monitoring systems, it is essential that the connection between the object under monitoring and the place of reception of the response should function reliably. In prior art, a solution is known in which the state of the object under monitoring is checked via a telephone connection. Line monitoring is accomplished simultaneously; if the connection between the two points is functional, then it can be assumed that the line is also functional. However, for each check it is necessary to make a call, open an audio line, which means that the telephone network will charge for the pulse produced. In the case of frequently repeated checks, the costs are considerable. In addition, in the solution in question, the operation of a robot telephone can be interfered with by calling the number of the robot telephone from an ordinary telephone and leaving the line busy. In another solution, the state of a network termination unit can be monitored by technical means from a telephone exchange. In this case, however, the monitoring does not cover the line from the network termination unit to the terminal adapter and the object under monitoring.
The object of the present invention is to eliminate or at least to significantly alleviate the drawbacks referred to above. A further object of the invention is to disclose a new type of method, system and associated terminal equipment for monitoring the line between an object under monitoring and the place of reception of the response. The invention enables reliable line monitoring without call charges resulting from opening a call.
The invention concerns a method for line monitoring in a monitoring system. The monitoring system comprises a telephone network, a master terminal connected to the place of reception of the response and to the telephone network, and a slave terminal connected to the object under monitoring and to the telephone network. The telephone network may be e.g. an integrated services digital network ISDN. The method of the invention comprises two main steps, a control call by the master terminal to the slave terminal and an acknowledgement call by the slave terminal. The setup of the control call is started from the master terminal to the slave terminal. The slave terminal identifies the control call originated by the master terminal on the basis of a predetermined call procedure before answering the call. The slave terminal does not answer the call and the call setup procedure is terminated.
The setup of the acknowledgement call from the slave terminal to the master terminal is started upon the lapse of a certain length of time after the control call. A suitable time may be immediately after the control call or after a predetermined delay. The master terminal identifies the acknowledgement call of the slave terminal on the basis of a predefined ringing procedure before answering the call. The master terminal does not answer the call but terminates the call setup procedure.
In a preferred embodiment of the invention, the B-party""s terminal, i.e. the terminal of the receiver of the call, identifies the A-party number transmitted in the signalling sent by the A-party, i.e. the originator of the call. In an embodiment, call setup is terminated by the A-party""s terminal after the A-party has received an ALERTING message. The A-party may be either the master or the slave terminal, each in its turn. From the B-party number transmitted in conjunction with the ALERTING message, the master terminal can verify that the call has been connected to the right slave terminal.
The ISDN network allows call setdown by the B-party as well. In an embodiment, the setup of the acknowledgement call is terminated by the master terminal after the master terminal has received a SETUP message from the slave terminal. In this case, the acknowledgement is obtained faster because the slave does not have to wait for an ALERTING message from the master.
Especially in burglar alarm applications, it is, important that fooling the monitoring line be as difficult as possible. In an embodiment, to improve the identity protection of the terminal, the terminal adapter comprised in the terminal is indicated via multiple subscriber numbering (MSN). The terminal adapter is connected to the network termination unit via an S-interface. In an embodiment, the properties of the B-party terminal are checked by means of a Low Layer Compatibility information element (LLC) included in the SETUP message, thus providing a further improvement in identity protection. The data in the LLC information element may include the type of the receiving telecommunication terminal, which is known to the telephone exchange. The exchange will not connect the call if the data in the LLC information element is different from the terminal type. In a preferred embodiment of the method, an alarm is issued if the ringing procedure deviates from a predetermined procedure. The alarm may be delivered by either one of the terminals.
The invention additionally concerns a line monitoring system used to monitor the line between the object being monitored by a monitoring system and the place of reception of the response. The system comprises an ISDN network, a master terminal, which is connected to the place of reception of the response and to the integrated services network, and at least one slave terminal, which is connected to the object to be monitored and to the integrated services network. In the system of the invention, the slave terminal comprises means for identifying a control call originated by the master terminal before answering he call, and means for starting the setup of an acknowlegement call from the slave terminal to the master terminal upon the lapse of a suitable length of time after the control call. The master terminal comprises means for identifying am acknowledgement call originated by the slave terminal before answering the call and means for activating an alarm function when the ringing procedure differs from a predetermined procedure. In an embodiment of the system, the master terminal comprises means for ringing a control call at a predetermined instant of time. The predetermined instant of time is e.g. a recurrent point of time or a given interval of time after the previous control call, the master polling one or more slaves at said instant.
The invention also concerns a master terminal for a monitoring system. It comprises a network termination unit connected to an integrated services digital network via a U-interface, a terminal adapter connected to the network termination unit via an S-interface, and an element connecting the terminal adapter to the place of reception of the response. The master terminal of the invention comprises means for establishing a control call to a slave terminal, means for terminating the control call before the call has been set up, means for identifying an acknowledgement call originated by the slave terminal and leaving it unanswered, and means for activating alarm function when the ringing procedure deviates from a predetermined procedure. The master terminal preferably comprises means for identifying a slave terminal on the basis of the A-party number.
A master terminal according to the invention comprises means for terminating call setup upon the reception of an ALERTING message from the slave terminal. The ALERTING message preferably comprises the number of the B-party, so the master will know that it is terminating the right call. A master terminal comprises means for terminating call setup upon the reception of a SETUP message from the slave terminal
A master terminal according to the invention comprises means for including in the SETUP message a Low Layer Compatibility information element corresponding to the properties of the slave terminal. In an embodiment, the terminal adapter connected to the network termination unit via an S-interface is indicated via multiple subscriber numbering. In an embodiment, the master terminal comprises means for ringing a control call at a predetermined instant of time.
The invention further concerns a slave terminal for a monitoring system, comprising a network termination unit fitted for connection to an integrated services digital network via a U-interface; a terminal adapter connected to the network termination unit via an S-interface; and an element connecting the terminal adapter to an object under monitoring. According to the invention, the slave terminal comprises means for identifying a control call originated by a master terminal and for leaving it unanswered; and means for establishing an acknowledgement call to the master terminal in a predetermined manner. The slave terminal preferably comprises means for identifying the master terminal on the basis of the A-party number.
In an embodiment, the slave terminal comprises means for terminating call setup upon the reception of an ALERTING message. The slave terminal comprises means for disconnecting the call when an unknown A-party is calling, thus making it impossible for any outsider to keep the telephone line busy. The slave terminal also comprises means for activating an alarm function when the ringing procedure deviates from a predetermined procedure, thus making it possible to take the effect of e.g. sabotage, mischief or malfunctions on the monitoring system into account.
As compared with prior art, the invention provides the advantage that the state of a slave terminal connected to an object under monitoring can be monitored remotely via a telephone network without incurring call charges. The invention makes it possible to monitor the line all the way from the point of reception of the response to the object under monitoring. The invention does not require any changes in the existing exchange equipment, but it can be utilized independently of the network operator. Moreover, the telephone line can also be used for normal calls because the terminals do not answer calls received from a known address or answer only after the lapse of a given waiting time.